A Multiple Input Multiple Output (MIMO) scheme refers to a scheme for improving data transmission/reception efficiency using multiple transmit antennas and multiple receive antennas, unlike a scheme using one transmit antenna and one receive antenna. That is, a transmitter or a receiver of a wireless communication system uses multiple antennas so as to increase capacity or improve performance. The MIMO scheme may be called a multiple antenna technique.
In the multiple antenna transmission technique, there are a single codeword (SCW) scheme for simultaneously transmitting N data streams using one channel encoding block and a multiple codeword (MCW) scheme for transmitting N data streams using M (here, M is always equal to or less than N) channel encoding blacks. At this time, each channel encoding block generates an independent codeword and each codeword is designed to facilitate independent error detection.
In a system for transmitting multiple codewords, a receiver needs to inform a transmitter of success/failure of detection (decoding) of each codeword. Thus, the receiver may transmit a hybrid automatic repeat request (HARQ) ACK/NACK signal for each codeword to the transmitter.
In case of uplink data transmission through a single antenna, single codeword (SCW) transmission can be supported. In addition, a synchronous HARQ scheme can be applied to single antenna uplink transmission, and an adaptive or non-adaptive HARQ scheme can be utilized according to whether a modulation and coding scheme (MCS) is changed during retransmission.